The goal of this interdisciplinary proposal is to determine the roles and mechanisms of action of large molecular forms of cholecystokinin (CCK) in prolonging the length of the postprandial intermeal interval (IMI) during normal feeding. We will establish the molecular forms of CCK within intestine and those released by a meal into portal and systemic blood, using state-of-the-art peptidomic technology we have developed. Based on persuasive recent findings, we predict that CCK-58 will be the critical probe. To establish a normal meal pattern, a spontaneously-feeding, undisturbed rat preparation will be utilized. To track sequential meals and intermeal intervals, we will employ a reliable and valid technique of behavioral observation; to permit the microstructural analysis of individual meals, we will also record second-by second intakes of solid food, using automated recording. To establish the physiological status of circulating CCK-58, the exogenous peptide (at physiological levels) and its selective receptor antagonists and agonists will be evaluated. Endogenous CCK will also be released using a specific CCK releaser, camostat and feeding patterns analyzed with and without selective antagonists. Potential central sites of action stimulated by exogenous CCK-58 will also be established by the use of vagotomy, Fos-like immunoreactivity and binding or radioactive CCK forms to central sites. The refined behavioral analyses and peptide biochemistry presented in this proposal will provide a decisive test of the hypothesis at risk: two locations of the CCK1 receptor control total daily food intake: the receptors at vagal afferents that regulate meal size and the receptors in specific regions of the brain that regulate IMI. The results of these investigations should further our understanding of how CCK regulates total daily food intake and demonstrate if CCK-58 could be an effective weapon in our fight against obesity. PUBLIC HEALTH RELEVANCE: Obesity is a common clinical problem. This disease results from poor control of food intake and the regulation of this process is poorly understood. The proposed research will investigate the role of the hormone cholecystokinin in the regulation of food intake.